The present invention relates to a method for manufacturing a motor including a stator core and a rotor core that are formed by stacking magnetic metal plates.
As shown in FIG. 12, one type of a conventional motor includes a stator core 1 that is formed by stacking magnetic metal plates and a rotor core 2 that is also formed by stacking magnetic metal plates. The stator core 1 is a stack of stator core sheets 3, each formed by pressing and punching sheet metal. The rotor core 2 is also a stack of rotor core sheets 4, each formed by pressing and punching sheet metal.
A rotation shaft 5 is inserted through the rotor core 2 to form a rotor 6. The two ends of the rotation shaft 5 are rotationally supported by a frame. The stator core 1 generates magnetic force that rotates the rotor 6. The rotation shaft 5, which is rotated together with the rotor 6, outputs a certain rotation force.
In such a motor, magnetic plates 7 are coupled to the two axial ends of the stator core 1. Each magnetic plate 7 has an L-shaped cross-section to form a rotor opposing portion 8 that reduces leakage flux and increases the output of the motor.
Japanese Laid-Open Patent Publication No. 2014-147177 discloses a motor that includes magnetic plates like those described above on a stator core.
In a motor such as that described above, the stator core sheets 3 and the rotor core sheets 4 are formed by punching the same magnetic steel sheets. The rotor core sheets 4 are punched at inner sides of the portions where the stator core sheets 3 are punched, and the stator core sheets 3 and the rotor core sheets 4 are punched one at a time. Such a pressing process is repeated to manufacture the same number of the stator core sheets 3 and the rotor core sheets 4.
However, the magnetic plates 7 increase the axial length of the stator core. Thus, more rotor core sheets 4 than stator core sheets 3 are necessary to form the rotor core 2. Hence, when the stator core sheets 3 and the rotor core sheets 4 are punched from the same magnetic plate, there will not be enough rotor core sheets 4, that is, there will be lacking sheets 4a. 
When pressing the rotor core sheets 4 and the stator core sheets 3 in accordance with the required number of the rotor core sheets 4, unnecessary stator core sheets will be produced. This increases the manufacturing cost.
In the above-described publication disclosing the motor, there is no reference to the manufacturing of the lacking rotor core sheets.